BAGHDAD, Iraq (CNN) -- The Pentagon's upcoming report to Congress on the Iraq war is expected to highlight a decline in violence in 2008, according to two Pentagon officials with knowledge of the report's contents.

"Measuring Stability and Security in Iraq," which could be released as early as Monday, covers activity from mid-February to mid-May.

Attacks on U.S. and Iraqi forces and U.S. military and civilian casualties are lower than in previous periods, the officials said.

CNN reporting shows that 19 troops were killed in May, the lowest monthly total since the start of Operation Iraqi Freedom. Eighteen U.S. troops have been killed in June.

The details were released Friday amid reports that coalition troops killed four militants in northern Iraq during a shootout with gunmen on rooftops.

The U.S. military said that near Balad, the gunmen ambushed coalition troops who were targeting a financial supporter of "a bombing network in the Tigris River Valley."

The troops returned fire, killing four attackers, including one who was wanted and linked to weapons trafficking.

The attack came as troops targeting al Qaeda in Iraq detained 30 suspected terrorists in Baghdad and Mosul on Thursday and Friday, the military said.

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"These precision operations will continue until al Qaeda and other extremist organizations stop their indiscriminate violence against the Iraqi people," said Maj. John Hall, a military spokesman.

Mosul is the capital of Nineveh province, where U.S. and Iraqi troops last month launched an offensive -- called Mother of Two Springs -- against al Qaeda in Iraq.

Also, in western Baghdad on Friday, at least three people were killed and 10 injured when a bomb in a parked car detonated near a restaurant. The bombing happened shortly before 9 p.m. in a commercial area in al-Harthiya neighborhood, according to an Iraqi Interior Ministry spokesman

In Mosul, a suicide car bomb in the eastern section of the city detonated near a checkpoint Friday, wounding at least five policemen.

And in Diyala province, a coalition soldier was killed and five were wounded Friday in three roadside bomb attacks on coalition patrols, the U.S. military said.

In southern Iraq, Iraqi-led troops were continuing a push against militants in the southeastern Shiite province of Maysan.